US 20090112427 A1
A method for operating a powertrain, including an electro-mechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine, includes monitoring slip across a selectively applied clutch within the transmission to indicate a clutch slip event, and if the monitoring indicates the clutch slip event decreasing a load across the selectively applied clutch by reducing torque of at least one of the engine and the electric machine, in order to reduce the slip, thereby ending the clutch slip event.
1. A method for operating a powertrain comprising an electromechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine adapted to selectively transmit mechanical power to an output member, the method comprising:
monitoring slip across a selectively applied clutch within said transmission to indicate a clutch slip event; and
if said monitoring indicates said clutch slip event, decreasing a load across said selectively applied clutch by reducing at least one of a magnitude of torque permitted from said engine and a magnitude of torque permitted from said electric machine, in order to reduce said slip, thereby ending said clutch slip event.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
initially reducing said magnitude of torque permitted from said engine to a magnitude of a calculated reactive clutch torque; and
progressively reducing said magnitude of torque permitted from said engine.
8. The method of
initially reducing said magnitude of torque permitted from said electric machine to said magnitude of said calculated reactive clutch torque; and
progressively reducing said magnitude of torque permitted from said electric machine.
9. The method of
10. The method of
11. The method of
12. The method of
initially maintaining said load across said selectively applied clutch; and
progressively increasing said load until a normal load across said clutch is achieved.
13. A method for operating a powertrain comprising an electro-mechanical transmission adapted to selectively transmit mechanical power to an output member through selective application of a plurality of clutches, wherein said transmission is mechanically-operatively coupled to an internal combustion engine and a plurality of electric motors, the method comprising:
monitoring clutch slip across each selectively applied clutch; and
if said monitoring indicates clutch slip in excess of a threshold clutch slip level through a slip detection period, limiting a magnitude of torque permitted from said engine transmitted through said clutches and limiting a magnitude of torque permitted from said electric motors transmitted through said clutches.
14. The method of
15. The method of
wherein said limiting said magnitude of torque permitted from said engine comprises
initially constraining said magnitude of torque permitted from said engine to a magnitude of a calculated clutch reactive torque, and
progressively constraining said magnitude of torque permitted from said engine; and
wherein said limiting a magnitude of torque permitted from said electric motors comprises
initially constraining said magnitude of torque permitted from said electric motors to said magnitude of said calculated clutch reactive torque, and
progressively constraining said magnitude of torque permitted from said electric motors.
16. Apparatus for operating a powertrain comprising an electro-mechanical transmission adapted to selectively transmit mechanical power to an output member through selective application of a plurality of clutches, wherein said transmission is mechanically-operatively coupled to an internal combustion engine and a plurality of electric machines, the apparatus comprising:
a control system monitoring slip across said clutches and including logic diagnosing excessive slip in each clutch and imposing torque constraints upon said engine and said electric machines based upon said diagnosis, said constraints being effective to reduce a load upon said clutch and eliminate said excessive slip.
17. The apparatus of
a command initially limiting a magnitude of torque permitted from said engine to a magnitude of a calculated clutch reactive torque; and
subsequent commands progressively constraining said magnitude of torque permitted from said engine.
18. The apparatus of
a command initially limiting a magnitude of torque permitted from said electric machines to a magnitude of a calculated clutch reactive torque; and
subsequent commands progressively constraining said magnitude of torque permitted from said electric machines.
19. The apparatus of
wherein said logic diagnosing excessive slip in each clutch further diagnoses an end to said excessive slip; and
wherein said logic imposing torque constraints upon said engine and said electric machines based upon said diagnosis, upon diagnosing said end to said excessive slip, issues control commands comprising
a command initially maintaining a load across said selectively applied clutch, and
subsequent commands progressively increasing said load until a normal load across said clutch is achieved.
This application claims the benefit of U.S. Provisional Application No. 60/982,458 filed on Oct. 25, 2007 which is hereby incorporated herein by reference.
This disclosure pertains to control systems for electromechanical transmissions.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known powertrain architectures include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. One exemplary powertrain includes a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Electric machines, operative as motors or generators, generate a torque input to the transmission, independently of a torque input from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.
Operation of the above devices within a hybrid drive vehicle require management of numerous torque bearing shafts or devices representing connections to the above mentioned engine, electrical motors, and driveline. Various control schemes and operational connections between the various aforementioned components of the hybrid drive system are known, and the control system must be able to engage and disengage the various components in order to perform the functions of the hybrid drive system. Engagement and disengagement is known to be accomplished through the use of a transmission employing clutches. Clutches are devices well known in the art for engaging and disengaging shafts including the management of rotational velocity and torque differences between the shafts. Engagement or locking, disengagement or unlocking, operation while engaged or locked operation, and operation while disengaged or unlocked operation are all clutch states that must be managed in order for the vehicle to operate properly and smoothly.
Implications to vehicle operation related to perceptible jerks or abrupt changes to vehicle acceleration are collectively described as drivability. One source of perceptible jerks affecting drivability is slip, or relative rotational movement between the connective surfaces of a clutch. Slip occurs whenever the reactive torque transmitted through the clutch exceeds the actual torque capacity created by the applied clamping force. Clutches can be designed to operate with some level of controlled slip in asynchronous operation, or clutches can be designed to operate with little or preferably no slip in synchronous operation. This disclosure deals with clutches designed primarily for synchronous operation. Slip in a transmission in synchronous operation results in unintended loss of control within the transmission and adverse affects to drivability. Another source of perceptible jerks affecting drivability results from changes in torque from torque generative devices. Input torque from the engine and input torque from the electric machine or electric machines in a hybrid powertrain can be applied individually or cooperatively to provide output torque. However, changes in total input torque required to meet torque demand, for instance, due to a change in operator pedal position or due to a transmission operating range state shift, must be handled smoothly. Particularly difficult to manage are input torques, applied simultaneously to a transmission, with different reaction times to a control input. Based upon a single control input, the various devices can change respective input torques at different times, causing increased abrupt changes to the overall torque applied through the transmission. Abrupt and uncoordinated changes to the various input torques transmitted through a transmission can cause unnecessary perceptible changes in acceleration or jerks in the vehicle, which can adversely affect vehicle drivability.
Clutches are known in a variety of designs and control methods. One known type of clutch is a mechanical clutch operating by separating or joining two connective surfaces, for instance, clutch plates, operating, when joined, to apply frictional torque to each other. One control method for operating such a mechanical clutch includes applying a hydraulic control system implementing fluidic pressures transmitted through hydraulic lines to exert or release clamping force between the two connective surfaces. Operated in this way, the clutch is not operated in a binary manner, but rather is capable of a range of engagement states, from fully disengaged and desynchronized, to synchronized with no clamping force applied, to engaged but with only minimal clamping force, to engaged with some maximum clamping force. The capacity of the clutch to transmit reactive torque is a function of the magnitude of the clamping force applied to the clutch. This variable control of clutches allows for smooth transition between locked and unlocked states and also allows for managing slip in a locked transmission.
A method to operate a powertrain comprising containing slip events by modulating input torques to the transmission would improve vehicle drivability.
A method for operating a powertrain, including an electro-mechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine adapted to selectively transmit mechanical power to an output member, includes monitoring slip across a selectively applied clutch within the transmission to indicate a clutch slip event, and if the monitoring indicates the clutch slip event decreasing a load across the selectively applied clutch by reducing at least one of a magnitude of torque permitted from the engine and a magnitude of torque permitted from the electric machine, in order to reduce the slip, thereby ending the clutch slip event.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The exemplary engine 14 comprises a multi-cylinder internal combustion engine selectively operative in several states to transmit torque to the transmission 10 via an input shaft 12, and can be either a spark-ignition or a compression-ignition engine. The engine 14 includes a crankshaft (not shown) operatively coupled to the input shaft 12 of the transmission 10. A rotational speed sensor 11 monitors rotational speed of the input shaft 12. Power output from the engine 14, comprising rotational speed and output torque, can differ from the input speed, NI, and the input torque, TI, to the transmission 10 due to placement of torque-consuming components on the input shaft 12 between the engine 14 and the transmission 10, e.g., a hydraulic pump (not shown) and/or a torque management device (not shown).
The exemplary transmission 10 comprises three planetary-gear sets 24, 26 and 28, and four selectively engageable torque-transmitting devices, i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutches refer to any type of friction torque transfer device including single or compound plate clutches or packs, band clutches, and brakes, for example. A hydraulic control circuit 42, preferably controlled by a transmission control module (hereafter ‘TCM’) 17, is operative to control clutch states. Clutches C2 62 and C4 75 preferably comprise hydraulically-applied rotating friction clutches. Clutches C1 70 and C3 73 preferably comprise hydraulically-controlled stationary devices that can be selectively grounded to a transmission case 68. Each of the clutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulically applied, selectively receiving pressurized hydraulic fluid via the hydraulic control circuit 42.
The first and second electric machines 56 and 72 preferably comprise three-phase AC machines, each including a stator (not shown) and a rotor (not shown), and respective resolvers 80 and 82. The motor stator for each machine is grounded to an outer portion of the transmission case 68, and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first electric machine 56 is supported on a hub plate gear that is operatively attached to shaft 60 via the second planetary gear set 26. The rotor for the second electric machine 72 is fixedly attached to a sleeve shaft hub 66.
Each of the resolvers 80 and 82 preferably comprises a variable reluctance device including a resolver stator (not shown) and a resolver rotor (not shown). The resolvers 80 and 82 are appropriately positioned and assembled on respective ones of the first and second electric machines 56 and 72. Stators of respective ones of the resolvers 80 and 82 are operatively connected to one of the stators for the first and second electric machines 56 and 72. The resolver rotors are operatively connected to the rotor for the corresponding first and second electric machines 56 and 72. Each of the resolvers 80 and 82 is signally and operatively connected to a transmission power inverter control module (hereafter ‘TPIM’) 19, and each senses and monitors rotational position of the resolver rotor relative to the resolver stator, thus monitoring rotational position of respective ones of first and second electric machines 56 and 72. Additionally, the signals output from the resolvers 80 and 82 are interpreted to provide the rotational speeds for first and second electric machines 56 and 72, i.e., NA and NB, respectively.
The transmission 10 includes an output member 64, e.g. a shaft, which is operably connected to a driveline 90 for a vehicle (not shown), to provide output power, e.g., to vehicle wheels 93, one of which is shown in
The input torques from the engine 14 and the first and second electric machines 56 and 72 (TI, TA, and TB respectively) are generated as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (hereafter ‘ESD’) 74. The ESD 74 is high voltage DC-coupled to the TPIM 19 via DC transfer conductors 27. The transfer conductors 27 include a contactor switch 38. When the contactor switch 38 is closed, under normal operation, electric current can flow between the ESD 74 and the TPIM 19. When the contactor switch 38 is opened electric current flow between the ESD 74 and the TPIM 19 is interrupted. The TPIM 19 transmits electrical power to and from the first electric machine 56 by transfer conductors 29, and the TPIM 19 similarly transmits electrical power to and from the second electric machine 72 by transfer conductors 31, in response to torque commands for the first and second electric machines 56 and 72 to achieve the input torques TA and TB. Electrical current is transmitted to and from the ESD 74 in accordance with whether the ESD 74 is being charged or discharged.
The TPIM 19 includes the pair of power inverters (not shown) and respective motor control modules (not shown) configured to receive the torque commands and control inverter states therefrom for providing motor drive or regeneration functionality to meet the commanded motor torques TA and TB. The power inverters comprise known complementary three-phase power electronics devices, and each includes a plurality of insulated gate bipolar transistors (not shown) for converting DC power from the ESD 74 to AC power for powering respective ones of the first and second electric machines 56 and 72, by switching at high frequencies. The insulated gate bipolar transistors form a switch mode power supply configured to receive control commands. There is typically one pair of insulated gate bipolar transistors for each phase of each of the three-phase electric machines. States of the insulated gate bipolar transistors are controlled to provide motor drive mechanical power generation or electric power regeneration functionality. The three-phase inverters receive or supply DC electric power via DC transfer conductors 27 and transform it to or from three-phase AC power, which is conducted to or from the first and second electric machines 56 and 72 for operation as motors or generators via transfer conductors 29 and 31 respectively.
The aforementioned control modules communicate with other control modules, sensors, and actuators via a local area network (hereafter ‘LAN’) bus 6. The LAN bus 6 allows for structured communication of states of operating parameters and actuator command signals between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus 6 and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality such as antilock braking, traction control, and vehicle stability. Multiple communications buses may be used to improve communications speed and provide some level of signal redundancy and integrity. Communication between individual control modules can also be effected using a direct link, e.g., a serial peripheral interface (‘SPI’) bus (not shown).
The HCP 5 provides supervisory control of the powertrain, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the user interface 13 and the powertrain, including the ESD 74, the HCP 5 generates various commands, including: the operator torque request (‘TO
The ECM 23 is operatively connected to the engine 14, and functions to acquire data from sensors and control actuators of the engine 14 over a plurality of discrete lines, shown for simplicity as an aggregate bi-directional interface cable 35. The ECM 23 receives the engine input torque command from the HCP 5. The ECM 23 determines the actual engine input torque, TI, provided to the transmission 10 at that point in time based upon monitored engine speed and load, which is communicated to the HCP 5. The ECM 23 monitors input from the rotational speed sensor 11 to determine the engine input speed to the input shaft 12, which translates to the transmission input speed, NI. The ECM 23 monitors inputs from sensors (not shown) to determine states of other engine operating parameters including, e.g., a manifold pressure, engine coolant temperature, ambient air temperature, and ambient pressure. The engine load can be determined, for example, from the manifold pressure, or alternatively, from monitoring operator input to the accelerator pedal 113. The ECM 23 generates and communicates command signals to control engine actuators, including, e.g., fuel injectors, ignition modules, and throttle control modules, none of which are shown.
The TCM 17 is operatively connected to the transmission 10 and monitors inputs from sensors (not shown) to determine states of transmission operating parameters. The TCM 17 generates and communicates command signals to control the transmission 10, including controlling the hydraulic circuit 42. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques for each of the clutches, i.e., C1 70, C2 62, C3 73, and C4 75, and rotational output speed, NO, of the output member 64. Other actuators and sensors may be used to provide additional information from the TCM 17 to the HCP 5 for control purposes. The TCM 17 monitors inputs from pressure switches (not shown) and selectively actuates pressure control solenoids (not shown) and shift solenoids (not shown) of the hydraulic circuit 42 to selectively actuate the various clutches C1 70, C2 62, C3 73, and C4 75 to achieve various transmission operating range states, as described hereinbelow.
The BPCM 21 is signally connected to sensors (not shown) to monitor the ESD 74, including states of electrical current and voltage parameters, to provide information indicative of parametric states of the batteries of the ESD 74 to the HCP 5. The parametric states of the batteries preferably include battery state-of-charge, battery voltage, battery temperature, and available battery power, referred to as a range PBAT
Each of the control modules ECM 23, TCM 17, TPIM 19 and BPCM 21 is preferably a general-purpose digital computer comprising a microprocessor or central processing unit, storage mediums comprising read only memory (‘ROM’), random access memory (‘RAM’), electrically programmable read only memory (‘EPROM’), a high speed clock, analog to digital (‘A/D’) and digital to analog (‘D/A’) circuitry, and input/output circuitry and devices (‘I/O’) and appropriate signal conditioning and buffer circuitry. Each of the control modules has a set of control algorithms, comprising resident program instructions and calibrations stored in one of the storage mediums and executed to provide the respective functions of each computer. Information transfer between the control modules is preferably accomplished using the LAN bus 6 and SPI buses. The control algorithms are executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles are executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation of the powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event.
The exemplary powertrain selectively operates in one of several operating range states that can be described in terms of an engine state comprising one of an engine on state (‘ON’) and an engine off state (‘OFF’), and a transmission state comprising a plurality of fixed gears and continuously variable operating modes, described with reference to Table 1, below.
Each of the transmission operating range states is described in the table and indicates which of the specific clutches C1 70, C2 62, C3 73, and C4 75 are applied for each of the operating range states. A first continuously variable mode, i.e., EVT Mode I, or MI, is selected by applying clutch C1 70 only in order to “ground” the outer gear member of the third planetary gear set 28. The engine state can be one of ON (‘MI_Eng_On’) or OFF (‘MI_Eng_Off’). A second continuously variable mode, i.e., EVT Mode II, or MII, is selected by applying clutch C2 62 only to connect the shaft 60 to the carrier of the third planetary gear set 28. The engine state can be one of ON (‘MII_Eng_On’) or OFF (‘MII_Eng_Off’). For purposes of this description, when the engine state is OFF, the engine input speed is equal to zero revolutions per minute (‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gear operation provides a fixed ratio operation of input-to-output speed of the transmission 10, i.e., NI/NO, is achieved. A first fixed gear operation (‘FG1’) is selected by applying clutches C1 70 and C4 75. A second fixed gear operation (‘FG2’) is selected by applying clutches C1 70 and C2 62. A third fixed gear operation (‘FG3’) is selected by applying clutches C2 62 and C4 75. A fourth fixed gear operation (‘FG4’) is selected by applying clutches C2 62 and C3 73. The fixed ratio operation of input-to-output speed increases with increased fixed gear operation due to decreased gear ratios in the planetary gears 24, 26, and 28. The rotational speeds of the first and second electric machines 56 and 72, NA and NB respectively, are dependent on internal rotation of the mechanism as defined by the clutching and are proportional to the input speed measured at the input shaft 12.
In response to operator input via the accelerator pedal 113 and brake pedal 112 as captured by the user interface 13, the HCP 5 and one or more of the other control modules determine the commanded output torque, TCMD, intended to meet the operator torque request, TO
As mentioned above, clutch slip is an event which occurs when the load or torque applied across a clutch exceeds an actual torque capacity of the clutch. The torque applied overcomes the static frictional forces between the connective surfaces of the clutch, and the connective surfaces rotate relative to each other. One method to avoid clutch slip is to modulate the clamping force available to the clutch control mechanism, where a greater clamping force results in a greater actual torque capacity. However, increasing available clamping force, for example, by boosting pressure to a hydraulic clutch control system, has limitations. For example, electric motor torque can change more quickly than hydraulic pressure can be boosted, and a large change in electric motor torque in a short period of time could result in the motor torques exceeding the actual torque capacity at the existing hydraulic pressure. Also, abrupt changes in forces acting upon the driveline can cause slip events. As a result, a slip event could be well underway and have already adversely affected drivability before the hydraulic pressure is boosted to recover from the slip event. Additionally, the sum of all possible torques possibly seen within the transmission, including input torque from the engine, motor torque from an electric motor or a plurality of electric motors, and driveline torques, can still exceed a maximum achievable torque capacity available at a hydraulic systems highest pressure setting. An alternative method is disclosed whereby torques from various sources can be limited in response to a monitored clutch slip, such that slip events reaching a certain measured slip speed threshold initiates a clutch slip recovery event, wherein torques from the engine and from electric motors are reduced in order to facilitate the frictional forces within the clutch stopping or slowing to an acceptable level the clutch slip.
Managing output torque in order to maintain drivability is a priority in controlling a hybrid powertrain. Any change in torque in response to a change in output torque request applied through the transmission results in a change to the output torque transmitted to the driveline, thereby resulting in a change in propelling force to the vehicle and a change in vehicle acceleration. The change in torque request can come from operator input, such a pedal position relating an operator torque request, automatic control changes in the vehicle, such as cruise control or other control strategy, or engine changes in response to environmental conditions, such as a vehicle experiencing an uphill or downhill grade. By controlling changes to various input torques transmitted to a transmission within a hybrid powertrain, abrupt changes in vehicle acceleration can be controlled and minimized in order to reduce adverse effects to drivability.
As is known by one having ordinary skill in the art, any control system includes a reaction time. Changes to a powertrain operating point, comprising the speeds and torques of the various components to the powertrain required to achieve the desired vehicle operation, are driven by changes in control signals. These control signal changes act upon the various components to the powertrain and create reactions in each according to their respective reaction times. Applied to a hybrid powertrain, any change in control signals indicating a new torque request, for instance, as driven by a change in operator torque request or as required to execute a transmission shift, creates reactions in each affected torque generating device in order to execute the required changes to respective input torques. Changes to input torque supplied from an engine are controlled by an engine torque request setting the torque generated by the engine, as controlled, for example, through an ECM. Reaction time within an engine to changes in torque request to an engine is impacted by a number of factors well known in the art, and the particulars of a change to engine operation depend heavily on the particulars of the engine employed and the mode or modes of combustion being utilized. In many circumstances, the reaction time of an engine to changes in torque request will be the longest reaction time of the components to the hybrid drive system. Reaction time within an electric machine to changes in torque request include time to activate any necessary switches, relays, or other controls and time to energize or de-energize the electric machine with the change in applied electrical power.
A method is disclosed wherein reactions times of the engine and of the electric machine or machines within a hybrid powertrain are utilized to control in parallel a lead immediate torque request, controlling the engine, and an immediate torque request, controlling the electric machines, the torque requests being coordinated by respective reaction times in order to substantially effect substantially contemporaneous changes to input torque.
Because, as discussed above, changes to input torque from the engine are known to involve consistently longer reactions times than changes to input torque from an electric machine, an exemplary embodiment of the disclosed method can implement changes in torque request to the engine and the electric machine, acting in parallel as described above, including a lead period to the more quickly reacting device, the electric motor. This lead period may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict engine and electric machine operation, and a multitude of lead periods might be used by the same hybrid powertrain, depending upon different engine settings, conditions, operating and ranges and vehicle conditions. An exemplary equation that can be used in conjunction with test data or estimates of device reaction times to calculate lead period in accordance with the present disclosure includes the following relationship.
TLead equals the lead period for use in methods described herein. This equation assumes that two torque producing devices are utilized. TLead Reaction represents the reaction time of the device with the longer reaction time, and TImmediate Reaction represents the reaction time of the device with the shorter reaction time. If a different system is utilized, comprising for example an engine with a long lead period, a first electric machine with an intermediate lead period, and a second electric machine with a short lead period, lead periods can be developed comparing all of the torque generating devices. In this exemplary system, if all three torque generating devices are involved, two lead periods, one for the engine as compared to each of the electric machines, will be utilized to synchronize the responses in each of the devices. The same system at a different time might be operating with the engine off and disengaged from the transmission, and a lead period comparing the first electric machine and the second electric machine will be utilized to synchronize the responses in the two electric machines. In this way, a lead period can be developed coordinating reaction times between various torque generating devices.
One exemplary method to utilize lead periods to implement parallel torque requests to distinct torque generating devices in order to effect substantially simultaneous changes to output torque in response to a change in operator torque request includes issuing substantially immediately a change to the engine torque immediate request, initiating within the engine a change to a new engine output torque. This new engine output torque, in conjunction with the electric motor operating state, is still managed by the HCP in order to provide some portion of the total input torque to the transmission required to propel the vehicle. From the point that the engine torque immediate request changes, the lead period expires, described above taking into account the differences in reaction times between the engine and the electric machine. After the lead period, a change to torque requests issued to the electric machine or machines, managed by the HCP in order to fulfill a portion of the operator torque request, is executed, and the electric machine changes the electric machine operating state, and as described above, the changes to the input torques provided by the engine and the electric machine change substantially simultaneously.
One with ordinary skill in the art will also appreciate that an engine tends to react or change speed and torque relatively slowly in comparison to a control system, such as a hydraulic control system, changing clutch clamping pressure. Therefore, in a clutch control strategy limiting engine input torque to accommodate clutch capacity to minimize clutch slip and in order to maximize available engine input torque available to the vehicle, it is advantageous to limit engine torque only to the maximum achievable torque capacity and to modulate or increase clutch capacity as needed to utilize the engines full input torque. An increase in torque demanded of the engine can be met with a timely, corresponding increase to clutch capacity as needed up the maximum achievable torque capacity of the clutch.
Another contemplated method utilizes the estimated torque capacity curves to limit motor torque. One with ordinary skill in the art will appreciate that motor torque, in hybrid control strategies, can be used in a wide variety of functions, either individually, in parity with an engine, or acting in an opposite direction to the engine, the electric machines fulfilling a wide variety of functions. One with ordinary skill in the art will also appreciate that a motor tends to react or change speed and torque relatively quickly in comparison to a control system, such as a hydraulic control system, changing clutch clamping pressure. Therefore, in a clutch control strategy limiting motor torque to accommodate clutch capacity to minimize clutch slip and in order utilize the relative responsiveness of the motors to changing torque demands, it is advantageous to limit motor torque to the estimated torque capacity without modulating the clutch control system. In a vehicle utilizing the above mentioned exemplary clutch control strategies, engine and motor torques may be utilized within the physical limits of the clutch while taking advantage of the relative reaction speeds of the various hybrid drive components.
The aforementioned methods, limiting input torque from the engine and electric machine torques to corresponding estimated maximum or capacity clutch torques without causing clutch slip, are useful to control hybrid drive components, maximizing available torque available to the driveline while maintaining torque demand responsiveness by selecting a limiting strategy corresponding to the respective reactive speeds of the hybrid drive components. However, estimated maximum or capacity clutch torques and estimated reactive torques are calculations based upon available data and are not always accurate. As a result of deviations in actual vehicle conditions from conditions apparent in the available data, situations can occur where a clutch that is not expected to experience clutch slip does slip. As a result, the above mentioned clutch control strategies, intending to maintain the clutch in a locked state while attempting to take full advantage of the torque available from the various components of the hybrid drive system, can allow the clutch to slip.
A method is disclosed whereby additional limits are imposed upon input and motor torques in response to an indicated slip event, thereby lowering reactive torque transmitted through the clutch, so as to recover from the slip event and restore the clutch to a substantially locked state.
The maximum achievable torque capacity and TC-EST as described above represent limits to the ability of a clutch to transmit torque without slippage. These torque limits, mapping the capabilities of a clutch based upon estimated or calculated clutch capabilities, can be utilized in hybrid control strategies to facilitate hybrid drive operation, maximizing drivability by allowing operation of torque generating devices up to the estimated limits of clutch capabilities while maintaining system responsiveness to changes in torque commands. One contemplated method to be utilized in hybrid control strategies utilizes the maximum achievable torque capacity curves to impose limits upon input torque from the engine or from an electric machine.
As depicted in
The threshold slip speed as described in the above methods can be a simple value or may be variable depending upon vehicle conditions. The threshold slip speed can be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict clutch operation. Further, the implementation of the clutch reactive torque lead immediate maximum and the clutch reactive torque immediate maximum with relation to the calculated reactive torque at the initiation of the remediation response, the rate at which these limits to the torques are increased through the remediation response, and the rate at which these limits are relaxed after the termination of the remediation response can also be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict clutch and hybrid drive operation.
As previously disclosed in relation to
It is understood that modifications are allowable within the scope of the disclosure. The disclosure has been described with specific reference to the preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the disclosure.